Robert Michelot

Synthesis and cytotoxicity of gossypol related compounds.

Gossypol, gossypolone, reduced gossypol and new Schiffs bases of racemic gossypol and gossypolone were extracted or synthesized. Their cytotoxic activities on KB human cancer cells were determined. Gossypolone and the ethylamine derivative of gossypolone were the most active compounds (IC(50) in the micromolar range in both cases). The cytotoxicity of gossypol and gossypolone was increased when the tests were performed in the absence of serum and decreased when catalase as well as mannitol were added to the culture medium.

Studies on synthetic inhibitors of t-RNA methyl transferases: analogs of S-adenosyl homocysteine

Summary The structural analogs ( 1–10 ) of S-adenosyl homocysteine have been tested as inhibitors of a N-2 guanine methyltransferase and a whole methyltransferase extract, both isolated from rabbit liver with E. coli B and E. coli K 12 f met t-RNAs as substrates. Derivatives in which the amino function of the adenyl moiety had been completely substituted (SAH f) 9 or replaced by an hydroxyl (SIH) 10 were devoid of inhibitory activity. However, if one hydrogen atom was still linked to the N-6 atom, (N 6 methyl SAH 8 ), the product was still an efficient competitive inhibitor (Ki 60 moles). A chiral change or the replacement of the homocysteine chain by different analogs such as thio ethanol 4 , thio propanediol 6 , thio propionic acid 5 or D homocysteine 1c , led to products displaying inhibitory activity on the methyltransferases. For instance D SAH 1c was found to be a potent competitive inhibitor of the reaction (Ki 40 moles). The comparison of the inhibition values obtained with SAC 2, SA cysteamine 3 , SAEtOH 4 and SA propionic 5 suggests an important hydrogen type bond between the terminal amino function and the enzyme whereas the terminal carboxyl group did not contribute efficiently to the binding of the inhibitors to the enzyme.

New thioderivatives of gossypol and gossypolone, as prodrugs of cytotoxic agents.

New dithiane or dithiolane derivatives of gossypol and gossypolone were synthesized with dithiolethane or dithiolpropane in the presence of BF(3)/Et(2)O. These thioderivatives exhibited low toxicity on KB cells (human epidermoid carcinoma cells of the mouth). They react easily with electrophiles in aprotic solvents to regenerate gossypolone or to form dehydrogossypoldithianes and dehydrogossypoldithiolanes, which display higher toxicity on KB cells. In addition, the low toxicity of gossypol thioderivatives was reversed by nitric oxide donors in physiological media. These experiments suggest that gossypol and gossypolone dithianes and dithiolanes can be used as prodrugs that target tumor cells surrounded by high concentrations of nitric oxide.

Use of BOP-Cl in the presence of Boc-amino monothioacids for the thioacylation of iminoacid residues

BOP-Cl was found to be an efficient coupling reagent for the introduction of thiopeptide bonds on imino acid residues (Pro, Sar). Boc-amino monothioacids were coupled at moderate temperature (0 degree C-RT) with fair yields and with retained optical purity. The mechanism of the coupling reaction is discussed.

N-acylated pentapeptides antagonists of substance P on guinea-pig ileum.

Summary Pentapeptides X-D,Trp-Phe-D.Trp-Leu-Y-NH2 (X = H, Boc, parachydroxyphenylacetyl, Y = Met,Leu,Nle,Phe) were tested as antagonists against Substance P and against a specific agonist of the muscular receptor of neurokinins on the guinea-pig ileum . Weak antagonist or agonist activities could be observed with the free or the Boc-protected pentapeptides whilst the acylated compounds could be compared favorably with the best antagonists already described.

Activity of the C-terminal part of substance P on guinea pig ileum and trachea preparations I. N-acylated pentapeptides SP(7–11)

Abstract Acylated pentapeptide XPhePheGlyLeuMetNH2 analogs of the substance P (7–11) sequence were synthesized by solution method and their spasmogenic activities were evaluated on guinea pig ileum (GPI) and trachea (GPT). Pentapeptide SP(7–11) had the lowest potency and its N-acylation increased its activity in both tests, with some derivatives being more active than SP itself. Results obtained on GPI suggest a close dependence of activity upon structural factors in the vicinity of the Phe7 N-terminus, whereas the activity on GPT seems more dependent upon the hydrophobicity of the analogs.

Nouvelles études de l'inhibition d'une tRNA N2 guanine méthyltransférase par des analogues de la S-adénosyl-homocystéine et de la S-adénosyl-méthionine

Summary New structural analogs of S-adenosyl homocysteine (SAH) ( 1–9, 11–14, 19–21 ) and of S-adenosyl methionine ( 15–18 ) have been tested as inhibitors of a N-2 guanine methyltransferase extract from rabbit liver with E. coli B tRNA as substrate. The sulfonium compounds (mixture of ± diastereoisomers) are more inhibitory than the sulfide derivatives but less inhibitory than SAH itself. The replacement of the aminoacid chain in SAH by various alphatic radicals leads to a correlation between their bulk and the size of the enzymatic site. The monosubstitution of N-6 amino group does not affect significantly the inhibitory effect, which is completely canceled by the disubstitution of N-6.

Design of potent dynorphin A-(1-9) analogues devoid of supraspinal motor effects in mice

Four analogues of dynorphin (Dyn) A-(1-9) incorporating D-Leu in position 8 alone or in combination with the nonhydrolysable psi [CS-NH] thiopeptide bond surrogate between positions 6 and 7 were tested in vitro for their ability to compete with the binding of selective kappa, mu, and delta opioid ligands, using membrane preparations of guinea pig cerebellum (kappa) and rat brain (mu and delta), for their ability to block the electrically induced contractions of the guinea pig ileum, and for their in vivo antinociceptive (writhing test) and motor (motor dysfunction assay) activities in mice. [D-Leu8]Dyn A-(1-9) displayed an affinity and a selectivity for the kappa opioid receptor that were comparable with those of Dyn A-(1-9). The potencies of [D-Leu8]Dyn A-(1-9) in the guinea pig ileum, writhing, and motor dysfunction assays were markedly enhanced (8-12 fold) compared with those of Dyn A-(1-9). [6 psi 7(CS-NH),D-Leu8]Dyn A-(1-9), [Lys6, 6 psi 7(CS-NH),D-Leu8] Dyn A-(1-9), and [Leu6, 6 psi 7(CS-NH), D-Leu8]Dyn A-(1-9) were somewhat less potent than [D-Leu8]Dyn A-(1-9) in all opioid assays. However, the thiopeptides were more potent analgesics than Dyn A-(1-9)(ED50 of 29.5, 23.9, and 15.5 nmol/mouse, respectively, compared with 90.7 nmol/mouse for Dyn A-(1-9)) and caused little or no motor impairment at analgesic doses.

Synthesis and biological activities of neurokinin pseudopeptide analogues containing a reduced peptide bond

A series of pseudopeptides, analogues of neurokinin selective agonists, in which a peptide bond was replaced by a (CH2NH) bond were synthesized. The biological activities of these compounds were determined on selective pharmacological preparations: the dog carotid artery for NK-1, the rabbit pulmonary artery devoid of endothelium for the NK-2 and the rat portal vein for the NK-3 receptors. The results reported in this study indicate that insertion of a pseudopeptide bond in various positions of these selective agonists resulted in a great decrease in potency compared to the parent compounds. Furthermore, the selectivity of agonists is maintained by the use of a methylene amino group in position 9–10 (Sar) for the NK-1 or in position 7–8 (MePhe) for the NK-3 selective compound. The selectivity is greatly diminished for the NK-2 analogues.

Nouvelles synthèses d'analogues de la S-adénosyl homocystéine et de la S-adénosyl-méthionine

Summary With the aim of studying analogues of S adenosyl homocysteine and S adenosyl methionine as potential inhibitors of methyl-transferases, we describe the syntheses of such analogues, in which either the amino-acid chain is replaced by various aliphatic radicals of the N 6 amino group of adenine is substituted.